Phosphorus dynamics and its uptake by wheat in salt-affected soils

Abstract

In some serious environmental constraints, soil salinity is a worldwide major issue for crop production and soil declination. Salinity in Pakistan has covered 6.68 million hectares area of cultivated land and further out of 6.68 million hectares 56% area is covered by saline sodic. The soil salinity causes hindrance in the availability of very essential macronutrients like phosphorus. The relation between phosphorus uptake and soil salinity is a complex phenomenon. With the aim to calculate phosphorus (P) fractions and to maximize P bioavailability in wheat crop, a series of pot and field experiments were conducted in normal and salt affected soils. In 1st incubation study rate of P was selected on the basis of plant available P at different time intervals from three different rates (200, 400 and 600 mg kg-1 of soil) of P fertilizer. Results revealed that among different fractions of P (bound and bioavailable), maximum Olsen-P was found 12.18 mg kg-1 in PROKA soil (saline sodic), 9.225 mg kg-1 in PARS soil (saline) and 9.125 mg kg-1 in UAF soil (normal), when P was applied at 400 mg kg-1 of soil. Selected rate of P fertilizer (400 mg kg-1) was used in 2nd incubation study with different organic amendments [farmyard manure (FYM), poultry manure (PM), crop residue (CR)] and sewage sludge (SS) for the determination of P fractions at different time intervals. Plant available Olsen-P fraction significantly increased after 90 days of incubation in all soils (normal, saline sodic, saline) with amendments FYM and PM but not as much with amendments CR and SS at P application level 400 mg kg-1 of soil. Overall, Olsen-P was increased maximum with PM (23.2, 21.7 and 19.4 mg kg-1) and FYM (20.6, 17.6 and 20.6 mg kg-1) as compare with SS (14.3, 15.5 and 15.7 mg kg-1) and CR (12.9, 14.4 and 14.0 mg kg-1) in normal, saline sodic and saline soils, respectively. To evaluate the effect of P rate (400 mg kg-1) selected from 1st study and organic amendments (FYM and PM) selected from 2nd study, A subsequent pot experiment was conducted in normal (UAF) and salt-affected (PROKA and PARS) soils. Results showed a significant effect on wheat growth, yield, physiological, chemical and biochemical parameters by combined application of P + PM in all soils. On the basis of these parameters, P + PM remained as best in normal and salt-affected soils with order of normal>saline>saline sodic. In pot experiment, maximum level of grain yield (24%), photosynthesis (37%), protein (20%), fat (40%), starch (41%) and maximum reduction in polyphenol (47%) were observed by combined application of P + PM, over control. Highest level of P in root xviii (53%), shoot (57%) and grain (121%) was found in wheat plant grown in normal soil while maximum level of Olsen-P (99%) was observed in saline sodic soil by P+PM treatment, over control. In field experiment, results showed that growth parameters such as plant height, root dry weight and 1000 grain weight were increased maximum with PM + P treatment in all soils. Photosynthetic parameters also affected significantly in all three types of soils by combined application of PM + P. Significant effect of combined application of P fertilizer and PM was recorded in case of P concentration in wheat root, shoot and grain in all soils. Biochemical parameters such as protein, fat, fiber, ash, starch and polyphenols were also affected significantly with treatment PM + P. Overall these experimental results showed that P fertilizer applied with PM, not only improved wheat growth, yield and physiology but also improved grain nutritional value and P uptake in both type of soils (normal and salt-affected). Reduction in adverse effect of soil salinity was also observed by integration of chemical fertilizers and organic amendments.